问题
leal(%eax,%ecx,4), %edx
as I was reading from my computer systems book, if there`s premises that $eax contains x value and %ecx contains y, then the above means, x+4y putting into %edx.
then if it is
movl(%eax,%ecx,4), %edx
, then isn`t the same one with leal expression above?
As I know, leal creates address that can be referenced,not referencing by itself like movl, but
when I saw leal(%eax,%ecx,4), %edx equals putting x+4y into edx register,
then doesnt it mean that it 'referenced'%eaxand%ecx` and extracted value x and y for using computation??
- doesn`t it "()" means 'referenced'??
回答1:
LEA loads an effective address generated by an address calculation into a register. MOV moves something somewhere, when using SIB addressing as source operand, it moves whatever is at the address generated by the address calculation into the target operand.
So:
leal (%eax,%ecx,4), %edx ← moves %eax+%ecx*4 into %edx
movl (%eax,%ecx,4), %edx ← moves whatever is at address %eax+%ecx*4 into %edx
来源：https://stackoverflow.com/questions/13517083/assembly-leal-and-movl-difference